Normal hexane and cyclohexane production



Aug. 2, 1966 w. o. scHELLENBx-:RG 3,264,361

NORMAL HEXANE AND CYCLOHEXANE PRODUCTION Filed May 1s, 1965 United States Patent O 3,264,361 NORMAL HEXANE AND CYCLO- HEXANE PRODUCTION Walter O. Schellenberg, Sweeny, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 13, 1963, Ser. No. 279,776 1 Claim. (Cl. 260666) This invention relates to the production of normal hexane. In one aspect the invention relates to the recovery of normal hexane from a petroleum fraction containing close-boiling constituent-s wherein the benzene `therein is hydrogenated and the eiiiuent therefrom is subsequently subjected to isomerization conditions to isomer-ine methylcyclopentane to cyclohexane.

Naturally occurring cyclohexane hydrocarbon fractions are very diicult to separate by fractionation from other closeeboiling constituents such as the dimethylpentanes, cyclohexane, normal hexane, isohexanes, benzene and methylcyclopentane.

A proposed method -for elfecting the production of high purity cyclohexane `from a naturally occurring petroleum fraction containing a mixture of close-boiling hexane constituents is by the isomerization of the methylcyclopentane to cyclohexane. =It is common practice to iirst treat the feed to the isomerization unit for the removal of isohexanes, naturally occurring cyclohexane and other impurities to leave normal hexane, methylcyclopentane and benzene. The benzene is then hydrogenated under benzene-hydrogenation conditions to cyclohexane with the eluent therefrom being the feed to the isomerization unit. Heretofore, it has been the practice to recover the methylcyclopentane from the isomerization unit eiiiuent and then subsequently recover the normal hexane therefrom as product. However, the normal hexane is isomerized in the isomerization unit to isohexanes, thereby reducing the amount of normal hexane recoverable.

It is `an object of the invention to provide an improved process for the recovery of normal hexane.

It is another object of the invention to provide an improved process for the isomerization of methylcyclopentane to cyclohexane.

It is yet another object of the invention to provide an improved process for the hydrogenation of benzene to cyclohexane,

These and other aspects of the invention will readily be apparent to those skilled in the art yfrom the accomrpanying disclosure, appended drawing and claim.

These objects are broadly accomplished by treating a benzene hydrogenation zone effluent containing normal hexane, methylcyclopentane, cyclohexane, and isohexanes so as to recover therefrom a fraction comprising normal hexane and isohexanes and leaving a second fraction comprising methylcyclopentane and cyclohexane W-ith the normal hexane product being separated from the isohexane. The second fraction is then passed to an isomerization zone under conditions wherein the methylcyclopentane is isomerized to cyclohexane with the cyclohexane being subsequently recovered.

In one embodiment the methylcyclopentane recovered from the isomerization zone eifluent is recycled to the feed to the hydrogenation unit.

The invention is best illustrated by the following draw- The drawing is a schematic illustration of the preferred embodiment employing the invention in the hydrogenation of a natural cyclohexane-containing feed also containing benzene and the subsequent isomerization of the methylcyclopentane in the hydrogenation efiluent.

Patented August 2, 1966 "ice A yfeed which has preferably been depentanized and deheptanized and comprising naturally occurring cyclohexane, normal hexane, methylcyclopentane, benzene and isohexanes is passed through conduits 2 and 4 into deisohexanizer 6 wherein the isohexanes are removed overhead through conduit 8. The bottoms from the deisohexanizer v6 :are `passed through conduit 10 into demethylcyclopentanizer 12. The cyclohexane and heavier products are removed as bottoms through conduit 16 tor passage into a separate process. The overhead 14 contains basically methylcyclopentane, lighter hydrocarbons, and a small amount of benzene which Kare introduced into the hydrogenation uni-t 1|8. Within .this hydrogenation unit, the benzene -is hydrogenated to cyclohexane in the presence of hydrogen with a suitable benzene hydrogenation catalyst such as nickel om kieselguhr, such as described in U.S. Patent No. 2,906,784, issued September 29, 9. The preferred catalyst is nickel-on-kieselguhr, the nickel content ranging from about 20 to about 55 weight percent of the catalyst. Preferably the temperature is maintained within a range of 370 to 550 F. with a pressure in the range of 400-'600 p.s.i.g. The eilluent from the hydrogenation unit 1,8 is then treated to remove hydrogen by passage through conduit 20 -into a fractionator 22 :wherein the hydrogen is removed overhead through conduit `24. The bottoms are removed through conduit 26 and are treated to remove the normal hexane bythe method of this invention. Heretofore, it has been the practice to pass the hydrogenation efHuent directly into the isomerization unit and then subsequently recover the normal hexane as solvent therefrom. However, this has the disadvantage of reducing the recoverable normal hexane since the normal hexane is isomerized to isohexanes within the isomerization unit. By the method of this invention the hydrogenation unit efuent is passed through conduit 26 into ydehexanizer 28 where-in the overhead product containing most of the isohexanes and normal hexane Iare removed through conduit 30 and passed into the ydeisohexanizer A32. The conditions are imaintained therein suitable for the distillation of the isohexanes overhead through conduit 34. The normal hexanes are removed as bottoms through conduit 3-6 and as a product. The bottoms from the dehexanizer 28 are passed through conduit 38 into an isomerization unit 40 wherein the methylcyclopentane is isomerized to cyclohexane. This isomerization unit is maintained under suitable conditions for the isomerization step an-d usually employes -a catalyst such as a catalyst of the platinum type, such as platinum-alumina promoted with chlorine or uorine. A particularly suitable catalyst is the Penex catalyst which is a platinum containing catalyst with alumina or another noble catalyst from the platinum group, such as ru'thenium, rhodium, palladium, osmium, iridium, and platinum promoted by a minor amount of a combined halogen. Preferably, the catalyst comprises a composite of alumina and platinum -with the platinum being in -a concentration of from 0.01 to about 5 percent by weight of the catalyst yand more particularly a composite of alumina, platinum and combined halogen, preferably iluorine. The catalyst may be `in the form of a powder, or larger size granules or may be regular size and shape. `Other suitable catalyst may be employed such as the aluminum halide type promoted by hydrogen chloride or the like.

When employing the Penex catalyst the temperature is preferably in the range of 650 to 750 F. with a pressure in the range of 400 to 550 p.s.i.g. and is sufficient to promote the isomerization of the methylcyclopentane to cyclohexane. The efuent from the isomerization unit is principally a mixture of methylcyclopentane and cyclohexane with smaller quantities of normal hexane and isohexanes. The effluent is passed through conduit 42 into vention, the methylcyclopentane-containing fraction is 4'. a third fraction containing cyclohexane from said second fraction leaving a fourthfraction` containing n-hexane, methylcyclopentane and benzene, passing ysaid fourth fraction through Ya hydrogenation 'zone under hydro- Aremoved overhead throughconduit 48 and back 'int-o the 5 genatio'n conditions suflicient to hydrogenate said benzene feed to the deisohexanizer 6 whichfis subsequently fed to cyclohexane, recovering a fthfraction ycontaining nto the 'hydrogen-ation unit 18. lv hexane and i-sohexane from theeflluent from said hydro- By thel method of this invention, the productionl of genation Vzone sand fle'aving a sixth fraction containingz normal hexane is increased due to a decrease in the isommethylcyclopentane',y recovering l.n-hexane product from erization ofthe normal hexane inthe isomerization unit .10, said fth '1"raction, passing said sixthfr'action -through an to is-ohexanes. In addition, by recycling the methylcycloisomen'zation zone .maintainedv underA isomerization conpentane to thehydrogenationunit. feed the isohexanes r ditions suflicient4 to isomerize .methylcyclopentane to lcytherein are removed. clohexane," recovering'cyclohexane product vfrom the* A material b-alance of one specific embodiment of the isomerization zoneI eluent--leaving a seventh fraction con- MoLs/DA'Y stream Y2 48 4 s 10 14 10` 20 24 26 30 38 34-y 35'Y 42 46 4s` Component: l Pentanesandlighter 50 50 Isohexanes 9,000 5,050 14, 050 13,450 600 600 000 50. 550- 500 50 350 150 Normalhexane. 8,300 3,300 11,0 35011,25011,^250 11,250 11 250 2,950 8,300 50 2,900 Benzene ,900 1,900 50 1,850 1,850 Methylcyelopentan 4,000 1,900 5,900 5,900 5,800 100 5,800 5,800 150 5,650 150 cyclohexane 1,000 300 1,300 ,300 80 1,220 1,930 ,9 1,930 Hepranes 800 800 800 40 760 40 40 4 i 1 91% nC. 2 97.5% cyclohexane; invention is presentedin the following table to better v taining methylcyclopentane, and recycling said seventh illustrate the invention. 30 fraction to said deisohexanizing zone. Y

While certain examples, structures, composition and. 4. process steps have been described for purpose of illustra- Refel'ellcesvclfed'bl th? Examlller tion, the invention is not limited to these. Variation and UNITEDSTATES .PATENTS modification within the scope of the disclosure and the v 440 7511E 5/1948 Le atski' 2609-666 f claim can readll be affected b those skilled 1n the art. 2 ,g

I claim: y y 3 2,906,784 9/1959'- Dean et--al 260-667 y A process for the recovery of n-hexane from a feed coni gonaldsol 7""78" 260%666 taining methylcyclopentane, benzene, isohexanes, n-hexi eau et a j 26o-666 ane, and cyclohexane comprising recovering a first fraction containing isohexaneffrom said feed in a deisohexanizing 40 zone leaving a second fraction containing methylcyclo pentane, benzene, n-hexane and cyclohexane, recovering DELBERT Ei GANTZ, Prmnry Examiner. f PAUL M. `CoUGHLAN,,Examinera V. OKEEFE, Assistant Examiner. 

